There is a wide commercial market available for the use of high performance electronic real time clocks. One significant feature requirement of high performance electronic real time clocks is the use of a crystal to generate the time base for the oscillator circuitry. For example, a conventional prepackaged crystal oscillator includes a quartz crystal to provide the frequency reference, and an oscillator amplifier to excite the crystal to resonance, while other crystal oscillator circuit packages utilize an external quartz crystal. However, as the consumer need for more powerful, smaller and less expensive electronic systems continues to be a driving force behind many new products and systems that don't need quite the accuracy of a crystal oscillator but do need a relatively precise oscillator, the cost and size of conventional crystal oscillator real time clocks make them prohibitive.
One solution to the conventional crystal oscillator has been through the use of the RC oscillator circuit. Although this has proven to be a somewhat acceptable solution for systems which require low performance oscillator circuits, it has fallen short for systems requiring more precise oscillator circuits. This is primarily because RC oscillator circuits are not very stable during operation. The reason RC oscillator circulates are not as stable as crystal oscillator circuits is due to the lack of a stable oscillator element for use by the conventional RC oscillator circuits to phase-lock to or to count down from. As with crystal oscillator circuits, another problem with conventional RC oscillator circuits is they take up too much valuable pc-board space.
One proposed solution to the above described problem with existing oscillator circuits is to utilize a crystal-less oscillator circuit having a frequency-locked loop feedback topology to generate an output signal having a stable frequency, such as the oscillator circuit described herein. However, one problem encountered with this crystal-less oscillator circuit is the fluctuation of the frequency of the output signal over varying temperatures of the device during operation. The frequency variations are a result of the temperature coefficients of a resistive element upon which the frequency of the output signal is dependent.
Accordingly, based upon the foregoing, it should be understood and appreciated that there is a need for a low power, monolithic crystal-less integrated circuit oscillator that provides an output signal with frequency stability approaching that of conventional crystal oscillators, and includes circuitry that provides compensation for the temperature coefficients of the frequency determinative elements therein.